Introduce a new `addresses' field that translates to passing `--address='
multiple times to dnsmasq.
* gnu/services/dns.scm (<dnsmasq-configuration>): Add an addresses field.
(dnsmasq-shepherd-service): Match the addresses field and translate it to
multiple '--address=' flags.
* doc/guix.texi (DNS Services): Document it.
Signed-off-by: 宋文武 <iyzsong@member.fsf.org>